The purpose of the proposed research, in response to NIA's Program Announcement regarding Harmonization of Longitudinal Cross-National Surveys of Aging (PAS-07-387) is to "harmonize" cognitive functioning measurement across four international surveys of aging - the HRS in the US, the English Longitudinal Study of Aging (ELSA), the European Survey of Health, Aging, and Retirement (SHARE), and the Korean Longitudinal Study of Aging (KLSoA). Impaired cognitive functioning, most often due to Alzheimer's disease and other dementias, is recognized as a major source of functional decline and loss of independence among older people. Cognitive functioning measures are now an integral part of the ongoing Health and Retirement Survey (HRS) and have been incorporated in other international longitudinal studies of aging modeled on the HRS. Measures vary substantially across surveys, however, and have received limited validation. Inclusion of cognitive assessments in international surveys of aging presents opportunities for cross-national comparisons of the role of cognitive impairment in independence, and of policy responses to needs for assistance of older cognitively impaired people, but only if the measurement equivalence of cognitive functioning across populations can be established. Item Response Theory (IRT) and Classification and Regression Tree (CART) are new measurement techniques that offer promising approaches to operationalizing equivalent measurement constructs for cognitive functioning and severe cognitive impairment across surveys and countries. Under IRT, comparable scores can be calculated for a measured construct even when different items are administered across groups. CART classifies items with regard to a dependent variable, and will be used to develop country specific algorithms that allow cross national comparisons of persons most impaired in everyday functioning due to cognitive deficits. Our aims in this project are 1) to first construct and evaluate standardized scores for global cognitive functioning and severe cognitive impairment, then 2) to use an IRT approach to generate cognitive functioning scores that demonstrate measurement equivalence across surveys, and 3) to use a CART approach to develop country- specific combinations of cognitive functioning items that exhibit similar expected impairment in everyday functioning across countries. By using these techniques to "harmonize" the disparate cognitive functioning items used across international studies of aging, this research provides the methodological underpinnings for valid cross-national comparisons of the role of cognitive impairment in health trajectories and the associated challenges to families and societies of providing assistance to older cognitively impaired individuals. PUBLIC HEALTH RELEVANCE: Project Narrative Impaired cognitive functioning, most often due to Alzheimer's disease and other dementias, is recognized as a major source of functional decline and loss of independence among older people. International longitudinal studies of aging are including measures of cognitive functioning, but measures vary substantially. This project applies new measurement techniques to develop equivalent measurement constructs for cognitive functioning and severe impairment across surveys, providing a foundation for future comparative cross-national research on care and service needs of older cognitively impaired individuals.